Microdosing is searched for three GLP-1 drugs at once, and each has its own page on this site. This one lays the three side by side: where each drug's labelled floor sits, the handful of randomised arms that fell at or below it, and what small amounts look like on a syringe. It adds no protocol and recommends no amount.
The detail for each molecule is on tirzepatide microdosing and semaglutide microdosing; retatrutide's trial ladder is on the retatrutide dosage page. GLP1Ledger's microdosing page covers who promotes the practice and why; this page stays with the figures.
The floors
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Lowest labelled or trial starting step | 0.25 mg weekly (Wegovy, Ozempic) | 2.5 mg weekly (ZEPBOUND, MOUNJARO) | 1 mg weekly (lowest phase 2 arm); 2 mg start in the escalating arms |
| Label status of that step | Initiation step, 4 weeks | Initiation only — "not approved as a maintenance dosage" | No label |
| Half-life | About 1 week | About 5 to 6 days | About 6 days |
"Below the floor" means very different milligrams for each drug: a tenth of semaglutide's starting step is 0.025 mg, a tenth of tirzepatide's is 0.25 mg. The ten-fold gap between the molecules' milligram scales is the first reason a single "microdose" figure cannot be carried from one to another.
The only randomised evidence at that scale
| Arm | Trial | Result | Placebo |
|---|---|---|---|
| Semaglutide 0.05 mg once daily (0.35 mg a week) | NCT02453711, 957 adults with obesity, 52 weeks | -5.99% body weight | -2.29% |
| Tirzepatide 1 mg once weekly | NCT03131687, type 2 diabetes, 26 weeks (PMID 30293770) | -0.9 kg | -0.4 kg |
| Retatrutide 1 mg once weekly | NCT04881760, obesity, 48 weeks (PMID 37366315) | -8.7% | -2.1% |
None of these arms was designed to test "microdosing"; each was the bottom rung of a dose-finding trial, and in each the higher arms went on to become, or to shape, the doses studied next. They are the only controlled data at that scale this site found. Beyond them the record is commentary: PubMed returned 10 records for microdosing with these drugs on 2026-10-01, and the relevant ones are letters, a perspective, a nurse-practitioner report and a narrative review.
What small amounts look like in units
Units on a U-100 syringe = mg ÷ mg/mL × 100. The concentrations below are the ones common for each molecule's research vials.
| Fraction of the starting step | Semaglutide at 2.5 mg/mL | at 5 mg/mL | Tirzepatide at 10 mg/mL | at 20 mg/mL | Retatrutide (of 2 mg) at 10 mg/mL | at 20 mg/mL |
|---|---|---|---|---|---|---|
| Half | 0.125 mg = 5 units | 2.5 units | 1.25 mg = 12.5 units | 6.25 units | 1 mg = 10 units | 5 units |
| Quarter | 0.0625 mg = 2.5 units | 1.25 units | 0.625 mg = 6.25 units | 3.1 units | 0.5 mg = 5 units | 2.5 units |
Most of these fall between the marks of a 1 mL barrel, which is marked in 2-unit steps, and several sit near the single-unit resolution of a 0.3 mL barrel. At 2.5 units, a one-unit misreading is a 40% error; at 1.25 units it is 80%. The concentration a vial is mixed to is therefore the main lever on precision at this scale — a weaker concentration turns the same milligrams into more units. The marks are explained on reading an insulin syringe and the formula on how milligrams become units.
Small weekly amounts still build up
A long half-life means each weekly injection adds to what remains of the last. With weekly dosing, the steady-state level is about 1 ÷ (1 − 0.5^(7 ÷ half-life in days)) times a single dose: about 2.0 for semaglutide (7-day half-life), 1.6 to 1.8 for tirzepatide (5 to 6 days) and 1.8 for retatrutide (6 days), reached after four to five half-lives. A "micro" weekly amount of semaglutide therefore settles at roughly twice its own size. The per-molecule clearance tables are on the semaglutide, tirzepatide and retatrutide half-life pages.
What is not established
No trial has tested microdosing as a practice for any of the three drugs. The three low arms above were in specific populations, for fixed durations, and are not evidence for any other amount. No equivalence exists between the molecules' milligrams. Nothing here is a dose or a plan; those decisions belong with a physician. The GLP-1 figures in one place are on the side-by-side GLP-1 dose table.
Sources and dates
Opened 2026-10-01: the ZEPBOUND label via openFDA (Eli Lilly, effective 2026-08-28), section 2 and 12.3; a WEGOVY label copy via openFDA (dosage and half-life); ClinicalTrials.gov v2 record NCT04881760; PubMed abstracts PMID 37366315 and 36354040; the PubMed microdosing search described above. NCT02453711 and NCT03131687 posted results as read for this site's semaglutide (2026-09-24) and tirzepatide (2026-09-23) microdosing pages. Units and accumulation factors are arithmetic by this site. Corrections go to the contact page.